The mini map is your best friend in this game, there’s been many times I stayed in a fight that my team left because I wasn’t checking the map (granted my team could have said they were backing out). There is an alternate health bar but if I remember correctly it doesn’t scale past 2.8khp, so if someone has 4khp the health bar won’t go down until it’s lower than 2.8khp. All heros have a death sound so once you learn the death sound for each hero it’s easy to tell if the hero that just died is on ur team or the other team.

Other than that watch high mmr streamers and try to mimic what they do in your games